EVERETT — A homeless man reportedly said he started a deadly Dec. 21 apartment fire by lighting up artificial trees and Christmas ornaments that were stacked near a stairwell, the only route to safety for many people who lived in the building.

William J. Matthews, 40, initially denied any involvement in the fire at the Colby Square apartments, but later described using a lighter to get it started and convincing himself nobody would get hurt, deputy prosecutor Robert Grant said in Snohomish County Superior Court papers filed Friday.

Matthews told a detective he set the fire because he was angry, needed help and was tired of living on the streets, Grant said in an affidavit filed along with a first-degree murder charge.

The defendant said he lives with post-traumatic stress from childhood and “that he just could not take it anymore, and the kid inside him said he needed to do something to cause a distraction and get attention that is negative,” the prosecutor wrote.

Flames spread from the stairwell at the center of the L-shaped building, blocking the escape route for people on the second floor. Tenants jumped from the balcony to escape. Some were elderly or disabled.

Elsie L. Flynn, 76, collapsed, suffered smoke inhalation and died later at an Everett hospital. The medical examiner determined her death was a homicide because the respiratory failure that ended her life was triggered by an arson.

Matthews became a suspect in the fire because of surveillance video in the neighborhood, court papers said.

The video captured a man wearing a backpack and a distinctive yellow-and-orange jacket at the apartment and then running from the stairwell shortly before flames and smoke were reported.

An Everett police officer was shown a still photograph from the video. He recognized Matthews from a previous disturbance call and said he had spotted the man walking near the apartments about 10 minutes before the fire, court papers said.

Matthews was tracked to Bellingham, where police found him near a freeway off-ramp.

He agreed to speak with an Everett detective. He reportedly said that after starting the fire, he ran away and went to a local park, court papers say. The recorded interview concluded when Matthews said he should probably talk to an attorney, according to documents filed earlier in the case.

The defendant is transient and faces a presumptive sentence of nearly 29 years in prison if convicted. The blaze caused damage estimated at between $800,000 and $1.5 million.

Matthews remained jailed Friday, his bail set earlier at $500,000.

Scott North: 425-339-3431; north@heraldnet.com. Twitter: @snorthnews.

Caleb Hutton / The Herald
William J. Matthews during a court appearance.